The isdndecode utility is part of
the isdn4bsd package and is used to provide the user with a
detailed mnemonic display of the layers 1, 2 and 3 protocol
activities on the D channel and hex dump of the B channel(s)
activities.

Together with two
passive supported cards and an easy to build cable it can also be
used to monitor the complete traffic on a S0 bus providing S0 bus
analyzer features.

The isdndecode
utility is only available for passive supported cards.

The following options
can be used:

−a

Run isdndecode
in analyzer mode by using two passive cards and a custom cable
which can be build as described in the file cable.txt in the
isdn4bsd source distribution. One card acts as a receiver for the
transmitting direction on the S0 bus while the other card acts as a
receiver for the receiving direction on the S0 bus. Complete
traffic monitoring is possible using this setup.

−b

switch B channel
tracing on (default off).

−d

switch D channel
tracing off (default on).

−f

Use filename as
the name of a file into which to write tracing output (default
filename is isdndecode<n> where n is the number of the unit
to decode).